Effect of lipid type, dispersed phase volume fraction and emulsifier on the physicochemical properties of nanoemulsions fortified with conjugated linoleic acid (CLA): Process optimization and stability assessment during storage conditions

Abstract

Conjugated linoleic acid (CLA) although gains recognition as food supplement due to various physiological activities, its water insolubility and oxidative instability limit its applications in food systems. Oil-in-water nanoemulsions based on extra virgin olive (EVOO) or pomace oil (OPO) are considered excellent delivery systems offering high protection and controlled release of CLA. In the present study, CLA-loaded nanoemulsions were prepared using ultrasonic homogenization approach and the effect of storage temperature (25 °C or 4 °C) on the nanoemulsion physical and chemical stability was investigated. All formulations demonstrated good long-term physical and chemical stability; mean droplet diameter <300 nm during 60 days-storage (4 °C and 25 °C). CLA degradation (RCLA %) was lower in the nanoemulsions with 8 wt% lipid phase; specifically, nanoemulsions with 8 wt% olive pomace oil and 6 wt% Tween 20 (RCLA = 80.154% at 25 °C and RCLA = 84.165% 4 °C) after 2 months. Response surface methodology was used to optimize the preparation conditions (type and concentration of lipid phase and emulsifier) at different storage conditions and predict the optimum values of mean droplet diameter, ζ-potential and CLA retention. The minimum lipid concentration (4 wt%) exhibited the optimum values at both environment and refrigerated storage for EVOO nanoemulsions. However, nanoemulsion with 8 wt% OPO and 4 wt% Tween 40 (71.843% at 25 °C) or 6 wt% Tween 20 were the optimum condition regarding the highest chemical stability.